It's not perfect, certainly, but the game stayed well-written to the end.  The reveal of who the killer was came as a genuine surprise to me, despite making sense in the context of prior events.  (And I am generally good at figuring these things out in movies.) 

The game itself pulls no punches.  You can indeed "lose" in that the kid you're trying to save can die if you screw up. and the protagonists can fail, and indeed, die.  One neat trick is that who the "hero" of the game is depends on what happens in the game.  I've played through three endings (by going back a few chapters, not replaying) and it is clear that issue of "hero" depends on who succeeds in the end.  It doesn't work perfectly...the "epilogues" at the end are a bit of a patchwork quilt...but the story itself makes "sense" even if it is character B who succeeds instead of the more obvious character A.

This is seriously an adult game, though, with some seriously disturbing moments, particularly witnessing the death of a child and a female character forced to strip at gunpoint.  This latter one is particularly disturbing because as the player, you have to take the actual actions in her shoes.  It's not a cut scene and I suspect you can fail and have really bad things happen.

Like a real movie, this game also handled moral choices well.  Too many games advertise having some sort of moral questions at the core, but too often these systems are overly binary and pointless.  Usually choices are obvious, and of little consequence other than marking you as "evil" or "good".  (For instance, in "Infamous", acting evil meant your lightening was red instead of blue and your abilities were slightly different.)  In "Heavy Rain", you are forced into a couple of moral choices for which the consequences are not obvious.  for instance, in "the lizard" chapter, you are are asked to kill a drug dealer in order to advance in the killer's tests to save your son.

The story is not perfect.  We have to accept that the police act in certain ways that real cops wouldn't act.  Beating of suspects.  Little consequence of killing a suspect.  But this is no worse than the most Hollywood movies.

In this sort of game (of which this is really the only example at the moment) the writing has to stand central as the game play in the end isn't all that interesting.  It is very much like an old adventure game without real puzzles.  A number of chapters involve characters wandering around trying to figure out which drawer to open.  Most of the action involves pressing whatever button when prompted.  (And in general, the action sequences are easy to pass.  I only failed at one.  My first run through I lost all four main characters, but in each case but one it was because I made a binary decision, with no time limit, incorrectly.

But in the end, the simplistic game play didn't matter because what was driving everything was story.  The fact that a particular section was just wandering trying drawers/closets/etc. to find evidence didn't matter because what was driving everything was that I really wanted to find that evidence.  In many ways, it matched reality.  Opening drawers is not hard in real life either, but the suspense of trying them when the bad guy might show up at any time was as nerve wracking in the game as it would be in life, despite the lack of challenge in the immediate actions.

I think the best advertisement for the game is that I immediately went back to see what other choices led to, and I am still going to be doing this over the next few days.

Parent notes (massive spoilers).  This game is not for kids.  Playing this game involves watching one ten year old die in a car crash and watching another drown.  (Maybe two if you screw up.)  Other scenes involve chatting with a prostitute, wandering around a party with drug use, a character having to choose whether to murder someone in cold blood, and a female character in her underwear being attacked in her by multiple knife wielding assailants.  As noted before, one harrowing scene, the heroine is forced to strip, at gunpoint, for a guy clearly interested in rape.  While this is not a morally ambiguous game like Grand Theft Auto (i.e. the goal is for the good guys to win and the bad guys to lose) I personally won't let my son play it until he is an older teenager.  It is very much the equivalent of a real R rated movie.